The days of searching in vain for someone's cell phone number are almost over. Starting early next year, consumers will be able to call directory assistance to get a mobile number.

Not every number will be listed in the directory being compiled by the Cellular Telecommunications & Internet Association, the trade group that represents wireless carriers. Wireless customers must give permission, or opt in, to be added.

And you'll have to call 411 to get a number; there won't be a directory in print or online.

Still, the service is drawing criticism from consumer advocates who say it encroaches on a rare bastion of privacy.

"These devices are considered much more personal than landline (phones),'' said Chris Hoofnagle of the Electronic Privacy Information Center. "People tend to carry them everywhere and answer them when they ring.''

Such concerns prompted Verizon Wireless, the No. 1 wireless company, to keep its 40 million subscribers out of the directory.

"We believe customers come to us with the expectation of privacy, and it's too early in the process to understand what releasing customer numbers to a database will mean,'' said Verizon Wireless spokeswoman Brenda Raney.

Promises are not enough for some lawmakers.

Rep. Joe Pitts, R-Pa., said most wireless service contracts include provisions granting permission to add a subscriber's number to a directory, absolving carriers of liability even if a customer does not opt in.

Though carriers say they'll modify the contracts, Pitts said,

"I don't want a promise. I want a law.''

A bill he introduced with Rep. Edward Markey, D-Mass., would require carriers to get existing customers' approval before adding their numbers to a directory. New subscribers could opt out or decline to participate when they sign up for service.

The bill also would prohibit charging fees to people who want to keep their numbers unlisted. Landline customers pay $2 to $3 a month for an unlisted number. A hearing on the bill is expected this fall.

Fears that mobile phone listings will violate privacy are overblown, said John Walls with the Cellular Telephone Industry Association. He cites the opt-in requirement, absence of a published directory and ban on sharing the list with telemarketers.

The list, he added, will be managed by an outside vendor; wireless carriers won't even see the subscriber numbers of their rivals. Cell phone customers can use caller ID to screen unwanted calls, and there will be no charge to keep numbers unlisted.

"We're looking at this as a customer benefit,'' said Sprint spokesman Scott Stoffel. "For customers that don't want this service, their numbers would remain private.''

Fueling the project is the fact that cell phones  163 million nationwide  rival landline phones in number. About 7 million people use only mobile phones.

A growing number of real estate agents, plumbers and others in small businesses who use mobile phones on the job are asking for a wireless directory.

Already, 5 million subscribers pay about $10 a month to publish their cell numbers in landline directories. It won't cost a dime to be in the wireless database.

Lee Brothers, owner of Arlington Lawn Service in Arlington, Va., said he would happily list his business cell phone number.

"Most of my business is done over the cell phone, and it's important for folks to be able to get in touch with me,'' he said.

But he would keep his personal cell phone off the rolls. "I'm skeptical about the telemarketing stuff. Anybody that really wants to get a hold of me, they have my number.''